KB: Some apps may not function after an enrolled Windows RT-based device is upgraded to Windows 8.1 RT

When you upgrade an enrolled Windows RT-based device to Windows 8.1 RT General Availability, all modern apps that were installed through the Company Portal app before the upgrade may not function immediately, and an "X" may be displayed on the apps tile.

This occurs because even though you can open the Company Portal app, you cannot use the apps that were installed from the Company Portal app until the device is connected to the Windows Intune service. After the device is connected, the Windows "side-loading" keys are re-provisioned and the functionality of the apps is restored.

For all the details for this issue as well as a resolution, please see the following: